It's the ultimate geek TV crossover that so many fans have dreamed about - Sherlock and Doctor Who. Steven Moffat and Mark Gatiss, the head writers on both shows, are clearly aware of that and dropped in a cheeky tease for fans of both shows that not everyone might have spotted.

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The YouTube fan video from James Kardatzke above reveals how Moffat and Gatiss added a cheeky Doctor Who reference in the credits to 'The Empty Hearse' earlier this year.

Keen-eyed viewers might have noticed that the letters spelling out Weng-Chiang were marked in red in the credits.

Old school Doctor Who fans will also know that there was an episode in the Tom Baker era titled The Talons of Weng-Chiang.